Highly Enantioselective Iron‐Catalyzed Sulfide Oxidation with Aqueous Hydrogen Peroxide under Simple Reaction Conditions

Abstract

Iron is one of the most abundant metals in the universe.[1] It is inexpensive, environmentally benign, and relatively nontoxic in comparison to other metals. For oxidation reactions the application of iron catalysts [2] in combination with aqueous hydrogen peroxide [3] would be most desirable. Asymmetric oxidations could then be achieved by the use of chiral iron complexes. In this context we recently reported a new enantioselective sulfide oxidation, [4][5][6] which provides optically active sulfoxides with up to 90 % ee.[7] The catalysis proceeds under very simple reaction conditions (at room temperature in a capped flask) and utilizes a readily available iron complex generated in situ from [Fe(acac) 3 ] and Schiff base 3.[8] Inexpensive and safe 30-35 % aqueous hydrogen peroxide serves as terminal oxidant (Scheme 1).Although the asymmetric induction in this iron-catalyzed sulfoxidation was remarkable, the practicability of the process was limited owing to the low conversion of 1. Thus, under the conditions required for high enantioselectivities, large amounts of unconverted sulfides remained, and the best yield of sulfoxide 2 was only 44 %. We now report on a significant improvement in this iron-catalyzed sulfide oxidation, leading to both higher enantioselectivities (up to 96 % ee) and better yields (up to 78 %).

Vanadium‐Catalyzed Asymmetric Oxidation of Sulfides Using Schiff Base Ligands Derived from β‐Amino Alcohols with Two Stereogenic Centers

“…Bolm found that an iron catalyst formed in situ by mixing Fe(acac) 3 and Schiff bases could efficiently catalyze this reaction. [10] By adding some acids or carboxylates into the catalyst system, the enantioselectivity increased to 66-96 %. [11] Strukul reported the chiral platinum diphosphane complex catalyzed oxidation of sulfides in water with surfactants.…”

Catalytic Synthesis of Triaryl Phosphates from White Phosphorus

“…Indeed, iron(III) acetylacetonate [Fe(acac) 3 ] has been used as a catalyst in a variety of oxidation reactions previously. The wide range of oxidizing agents (and substrates) used in conjunction with it include H 2 O 2 (used in stereospecific oxidations of sulfides), [17] high-pressure oxygen (oxidation of phenol) [18] and air (aerobic oxidation of the ethylene bond in β-isophorone). [19] In our application of iron(III) acetylacetonate as a catalyst (using the conditions mentioned above), a complete conversion of P 4 to triphenyl phosphate (with 100 % selectivity as assessed by 31 P NMR spectroscopy) was achieved.…”

Recent Progress in the Selective Oxidation of Sulfides withHydrogen Peroxide

“…随后, 他们尝试在反应体系中加入 取代苯甲酸及其盐类添加剂, 以期提高产率和对映选择 性. 和取代苯甲酸盐相比 [49] , 体系中加入取代苯甲酸添 加剂 [50] , 亚砜的产率和 ee 值提高的幅度比较大, 分别可 以达到 36%～78%和 66%～95%. 以四氢呋喃作溶剂, 三氟甲磺酸铈可以催化 50%的 过氧化氢选择性地氧化硫醚为亚砜 [56] .…”